The invention relates generally to gasification and combustion technologies and more specifically to methods and apparatus for low emissions combustion.
Integrated gasification combined cycle (IGCC) systems are a promising technology for power generation as they offer the possibility of producing electricity from abundant fuels such as coal biomass, pet coke, municipal waste and other fuel feedstock, with reduced emissions. An IGCC system typically includes an air separation unit (ASU), a gasification system and a gas turbine combined cycle system. Pressurized high purity oxygen is produced in the ASU and sent to gasifier. In the gasifier, fuel feedstock reacts with the oxygen in the presence of steam to produce syngas rich in carbon monoxide (CO) and hydrogen (H2). Syngas containing hydrogen is combusted in the combustor of the gas turbine combined cycle system. Current syngas combustors are diffusion burners and steam is usually used as a diluent to reduce thermal nitrogen oxide (NOx) formation. Using steam as a diluent in syngas combustion puts a limitation on the maximum turbine inlet temperature that can be achieved thus limiting the maximum efficiency.
Some of the challenges currently faced in commercializing IGCC systems for power generation include high capital cost compared to other power generation technologies such as pulverized coal plants. To improve the overall efficiency of the IGCC system, several integration schemes of the various subsystems are being explored. Some of these include supplying the steam required for syngas cleanup and combustion diluent from the heat recovery steam generator (HRSG) of the gas turbine system as well as compressing the air required for ASU using the compressor of the gas turbine.
Accordingly, there is still a need for further integration of the various sub systems of the IGCC system to increase the overall efficiency and a need for developing combustion technologies that allow higher turbine inlet temperatures without correspondingly increasing thermal NOx formation.